1. Field of the Invention
The present invention relates to a method of transmission of channel quality information (CQI) and apparatus for utilizing such method in a Multiple Input Multiple Output (MIMO) system, and more specifically, to a quantization method of transmission of channel quality information (CQI) based on values of codewords, and apparatus for utilizing such method in the Multiple Input Multiple Output (MIMO) system.
2. Description of the Related Art
In an Orthogonal Frequency Division Multiplexing (OFDM) system, data may be transmitted by a transmitter and received by a receiver. At the transmitter, the input data may be sequentially processed by a quadrature amplitude modulation (QAM) modulator, a serial-to-parallel convertor, an inverse fast Fourier transform (IFFT) unit, and a parallel-to-serial convertor and a cyclic prefix (CP) inserter. The resulting sequence of samples is referred to as OFDM symbol. At the receiver, the transmitted data from the transmitter is sequentially processed by a cyclic prefix remover, a parallel-to-serial convertor, a fast Fourier transform (FFT) transformer, a parallel-to-serial convertor and a QAM demodulator. And therefore, the transmitted data may be recovered at the receiver.
Multiple Input Multiple Output (MIMO) schemes use multiple transmitting antennas and multiple receiving antennas in order to improve the capacity and reliability of a wireless communication channel. A MIMO system promises linear capacity with K where K is the minimum of number of transmitting antennas (M) at transmitter and receiving antennas (N) at receiver. As one example, four different data streams Data Streams are transmitted separately from the four transmitting antennas. The transmitted signals are received at four receiving antennas. Spatial signal processing may be performed on the received signals by a spatial signal processor in order to recover the four received data streams.
In the contemporary specifications of the LTE (long term evolution), codewords may be employed and mapped to up to four data transmission layers in the MIMO transmission.
As an example, in a four by four MIMO system, two codewords may be employed. The feedback of channel quality information (CQI) in the case of two-codeword MIMO transmission has been discussed in several 3GPP (third Generation Partnership Project) RAN1 contributions. An employment of CQIbase and CQIdelta in the feedback of CQI is the preferred approach in the contemporary LTE, because it may reduce the feedback overhead in the uplink by assigning fewer feedback bits for CQIdelta than for CQIbase. Here, CQIbase is one of the two CQIs respectively defined for one of the two codewords respectively defined for each data transmission layer, and CQIdelta is a difference between the two CQIs.
Recent research, however, discovers that the performance loss of the above stated “CQIbase+CQIdelta” scenario may lead to potential performance loss in certain scenarios where the dynamic range of the CQIdelta may vary significantly in different configurations and channel situations. Therefore, the contemporary scenario of “CQIbase+CQIdelta” has a limited compression potential.